... may be something that uses the built-in camera to take a picture of your eye (the iris, specifically) and then uses that picture to seed a software random number generator on the basis of which it then creates you a PGP keypair, the public part thereof displayed as a QR, readily available to be emailed and so forth, whereas the private part is never displayed or even retrievable. As long as you hold that phone and remember your password you can use the key, and that's that.
This would allow for the fast and cheap creation of PGP keypairs (the significant entropy contained in the iris helping you get through the usual limitations of time needed to collect entropy) which could in principle be very short lived, as short lived as perhaps a few hours.
The concept could be expanded. For instance the only sensible way to open bank accounts that are accessible online is and will remain for you to register your PGP public key with the bank, along with your ID and whatever other paperwork they need. Having this smartphone application at the ready would allow you to create extremely secure short lived keys, good for perhaps that one day out of the entire month when you pay bills, among other very useful applications.
It doesn't even have to stop there, with decent eye recognition technology built in you could just as well get rid of the passphrase completely. Taking it one step further, you could even have a hardware item (which isn't a smartphone) that has two modes of operation. In mode 1, it takes a picture of your eye and creates a keypair, then encodes the eye ident data with the public key and stores the whole. In mode 2, it takes a picture of your eye, verifies that it matches the saved info and proceeds to either encrypt, decrypt or sign for you. The device recognises whether it has to operate in mode 1 or 2 by whether it has eye ident data stored (and once in mode 2 it can never be moved back to mode 1, or at least not easily, but in any case not without destroying the private key).
Obviously the strength of the entire thing would depend on the cryptographic strength of the app, but in principle this coupling of item + knowledge (since your passphrase is useless without your phone and your phone is useless - for this purpose - without your passphrase) correctly implemented would transform a smartphone into an actually useful item, for the first time in the history of smartphones. It's certainly the only thing that would make me contemplate buying one, at least from what I've heard and seen so far.
Anyone actually doing this ?